It has been known for a long time that a silver ion, a copper ion and a zinc ion have an antibacterial property. For example, a silver ion has widely been utilized as a disinfectant or a germicide in the form of a solution of silver nitrate. However, the use of silver nitrate as a form of solution is inconvenient for handling and further there is a fault that such a form can be used only for restricted purposes.
Then, a polymeric substance holding the metalic ions was proposed for a use of various fields to reduce the aforementioned disadvantages. Many methods of incorporating the metal ions into a polymeric substance are known, for example, a method of binding or adding fine wires or powder of the metals themselves to a polymer and a method of incorporating compounds of the metals into a polymer.
However, in such methods as mentioned above, in which the metals themselves are used, there is a disadvantage that the metals show poor compatibility because the specific weights and Young's moduli of the metals are usually very high compared with those of the conventional polymers.
In addition, such metals lead to a heavy weight of products and a high cost as they are necessarily used in a large amount. In a method wherein compounds of the metals are used, a product obtained can be utilized only for restricted purposes because of a heavy influence of the compounds on polymer properties, or else it shows poor durability of an antibacterial performance because the metal ions are merely contained in or attached to a polymer and, accordingly, they easily fall away from a polymer while being used.
For a method having no or less disadvantages as mentioned above, a method was proposed wherein a polymer contains organic functional groups having an ion exchange function or a complex-forming function and thereby these groups retain the metal ions. However, in this method, an adverse effect of these functional groups on physical properties of the polymer can not be disregarded.
Whether the functional groups are chemically introduced into the polymer or compounds having the functional groups are involved in a polymer, a type of polymer and a type and an amount of functional groups capable of being used are limited in order to avoid noticeable change of physical properties of polymers.